We have recently developed and evaluated a model for assessing coronary flow and myocardial metabolic factors in the newborn lamb. An important advantage of this model is that metabolic measurements are largely derived from the same components of the heart which generate the mechanical events recorded. Our initial studies will be extended to determine the relative contribution of carbohydrate and lipid substrate for myocardial energy production in the newborn and young lamb and to assess the effects of altered arterial blood glucose concentrations on myocardial substrate utilization, oxygen consumption and mechanical performance in the normal and hypoxic heart. Mechanisms of action of insulin and glucagon will be explored in this context. Influences of the autonomic nervous system on regulation of coronary flow, myocardial metabolism and cardiac function will be studied in the developing mammal with particular emphasis on direct and reflexly induced alterations of sympathetic neural function. The contributions of specific reflex systems including the peripheral chemoreceptors, the CNS ischemia response and the carotid sinus reflex will be studied and evidence for developmental changes will be sought. A major thrust will be to use this model to study the cardiovascular effects of the prostaglandins, the mechanisms of their hemodynamic actions and their influence on autonomic function in the developing mammal. The relationships of coronary perfusion pressure to coronary flow, myocardial oxygen consumption, substrate utilization and ventricular performance during systemic hypotension will also be explored. An intact model will be developed to extend these studies to the awake preparation.